1. Field of the Invention
The present invention relates generally to modems, and, more particularly, to a power conservation system for a modem in a computer system.
2. Description of the Related Art
Contemporary computer systems have a power saving or conservation feature which is automatically invoked when the computer is idle (not used) for a predetermined period of time. In a power conservation mode of operation, the computer is supplied with a minimum amount of power. Some computer systems have a hierarchy of different power conservation modes, e.g., idle, standby, and sleep modes of operation, which utilize a different amount of power, respectively. When use of the computer is resumed from a power conservation mode, the normal power supply is re-established. Modems (modulator/demodulator) utilized in such computer systems also have a power-saving function for minimizing power consumption.
With reference now to FIG. 1, there can be seen a block diagram of a conventional computer system having a power conservation feature. In general, the computer system includes a monitor 50, a main body 1, and a keyboard 2. The main body 1 includes a central processing unit (CPU) 20, a memory 30, a video logic module 40, a timer 60, a direct memory access (DMA) and interrupt controller 70, an expansion slot (or port) 80, a modem 10 coupled to the expansion slot 80, storage media 90 (e.g., a floppy disk drive and/or a hard disk drive and/or a CD-ROM drive), a power supply 110, an auxiliary power supply 120 (e.g., a secondary battery), and a power management system 100 for controlling the power supply 110 and the auxiliary power supply 120.
With additional reference now to FIG. 2, there can be seen a schematic diagram of the ring detect circuit of the conventional modem 10 having a power-saving function. The ring detect circuit includes a photocoupler 11 having an input terminal connected to ring signal lines G of a telephone line pair, and a phototransistor having a collector terminal connected to power voltage Vcc supplied through the expansion slot 80, an emitter terminal coupled to ground through a resistor, and a base terminal photocoupled to a light emitting diode (LED). An output terminal RI of the ring detect circuit is coupled to an output node disposed between the power supply Vcc and the collector terminal of the phototransistor of the photocoupler 11.
The ring detect circuit operates as follows. More particularly, when a ring signal is present on the ring signal line G, (e.g., when an incoming call is received), it is converted by the LED into an optical signal which is coupled to the phototransistor, which, in turn, converts it back into an electrical signal which is applied as an output ring detect signal to the output terminal RI. The photocoupler 11 thus minimizes the noise level of the ring detect signal by eliminating noise inherent in the ring signal applied over the ring signal line G. When the keyboard 2 is not used (i.e., data is not keyed in or inputted) for a predetermined period of time, the power management system (PMS) 100 switches the power supply 110 and the auxiliary power supply 120 from a normal (active) mode to a power conservation mode of operation in which a minimum amount of power is supplied thereby to the main body 1, and cuts off power to the rest of the computer system, including the modem 10. When the power supply to the modem 10 is cut off, the operation of the ring detect circuit 10 is discontinued, thereby minimizing power consumption. However, this conventional modem 10 suffers a major disadvantage, in that no incoming data can be received via the modem 10 while it is in the power conservation mode. In this regard, the modem 10 should ideally be in a standby mode at all times.
Korean Utility Model Unexamined Application Publication Nos. 94-8840 and -8841 (published on Apr. 21, 1994) propose a "Facsimile and Modem Having a Built-in Computer with a Power Controller of Telephone Incoming and Receiving Type", and "Telephone Operated Only to Facsimile and Modem", respectively, to overcome the above-described disadvantage of the conventional modem 10.
The 8840-41 publications disclose an integrated (unitary) fax/modem having a built-in computer and power controller, which utilizes a mechanical or electronic switch responsive to a detection signal produced by a current or voltage sensor which is indicative of unused, incoming call, and outgoing call states of the fax/modem. Thus, whether manned or unmanned, the telephone communication link of the fax/modem is not interrupted, since a current or voltage sensor is utilized which is not dependent upon an external power supply which is cut off during a power conservation mode of operation, rather than, as in the conventional modem 10, utilizing a photocoupler 11 which depends upon a power supply Vcc which is cut off during a power conservation mode of operation.
Although the above-described integrated fax/modem disclosed in the 8840-41 publications overcomes the major disadvantage of the conventional modem 10, it has other drawbacks and shortcomings. Namely, since the computer must always be in a standby mode of operation to perform the power control operation described above, it requires an external auxiliary adapter, which increases power management overhead and power consumption.
Based on the above and foregoing, it can be appreciated that there presently exists a need in the art for a power conservation system for a modem in a computer system which overcomes the above-described disadvantages, drawbacks, and shortcomings of presently available systems. The present invention fulfills this need.